The present invention relates to the field of intravascular radiation therapy. In particular, the present invention relates to catheters used for intravascular delivery of radiation.
Coronary artery balloon angioplasty is a minimally invasive technique developed as an alternative to coronary artery bypass grafting for treatment of atherosclerosis, the principle process of heart disease. There are about 450,000 coronary interventions, i.e., angioplasty, atherectomy, and stent, performed annually in the U.S. However, a major limitation of this clinical procedure is the high prevalence of restenosis, or re-narrowing, of the treated vessel. Restenosis occurs approximately 30-50% of the time.
Restenosis occurs as result of injury to the vessel wall due to the angioplasty procedure, or to other procedures, i.e., stenting, atherectomy, that compress or remove the atherosclerotic material and may cause trauma to the vessel. Restenosis is a complex process, which can involve an immediate vascular recoil, neointimal hyperplasia, and/or late vascular remodeling. Neointimal hyperplasia, a response of the body to balloon-induced physical injury of the vessel wall, is thought to be the main contributor to restenosis. Hyperplasia can result in narrowing of the vessel lumen within 3-6 months after angioplasty due to proliferation of smooth muscle cells in the region traumatized by the angioplasty. Restenosis can require the patient to undergo repeat angioplasty procedures or by-pass surgery with added costs and risks to the patient.
One method currently used to inhibit restenosis following a procedure such as angioplasty, involves delivery of a prescribed dose of radiation to the walls of the dilated length of vessel through intravascular radiotherapy (IRT). In an example of one method of IRT, a catheter is inserted into a vessel and positioned within the length of vessel dilated by the angioplasty procedure. Once the catheter is positioned, a radiation source is inserted into the lumen of the catheter and positioned to allow delivery of a prescribed dose of radiation to the vessel over a period of time. As a radiation source is relatively small, the radiation therapy may require the radiation source to remain positioned a minimum of four minutes in the vessel. To maintain the position of the catheter within the vessel, some IRT catheters are structured to engage the vessel walls until the radiation therapy is complete.
A consideration in the design of the above IRT catheters is the effect on blood flow in the vessel. If an IRT catheter is structured so that it obstructs blood flow within the vessel over a prolonged period, for example, more than one minute, this may result in impaired heart function, angina, cardiac arrest, or myocardial infarction. Should a low blood flow rate, e.g., a low perfusion flow rate, be detected, the IRT is typically stopped and the catheter withdrawn to allow the blood flow to reestablish and the area to recover. The IRT must then be restarted to complete the therapy session. This can result in a prolonged treatment period and discomfort to the patient.
Alternatively, if an IRT catheter is structured much smaller than the vessel diameter to allow a higher perfusion flow rate, the catheter may not adequately engage the vessel wall and the radiation source may not be centered such that the vessel would receive a non-uniform delivery of the radiation.
For a given radiation source, the intensity of the radiation drops rapidly as a function of distance from the source axis, i.e., a small change in distance from the source to the surface of the vessel wall can result in a large difference in the radiation intensity. Thus, if the radiation source is positioned close to the vessel wall, the wall may receive an overdose of radiation, e.g., a xe2x80x9chotxe2x80x9d spot develops. Overdosing a vessel wall with radiation can result in vessel damage, such as inflammation, hemorrhaging, and arterial necrosis. Conversely, the opposite side of the vessel may receive an underdose of radiation that may result in no inhibition of restenosis.
In order to mitigate both the effects of low perfusion flow rates and of overdosing or underdosing a vessel, other catheters, such as centering catheters have developed structures which compliantly engage, or self-fit within, the walls of the vessel to both deliver an approximately uniform dose of radiation and to maintain the catheter position within the vessel. Typically, portions of the catheter structure contact the vessel wall while providing openings for perfusion past the catheter.
U.S. Pat. No. 5,643,171 to Bradshaw et al. describes several embodiments of a centering catheter that may be used with IRT. In one embodiment, a centering balloon is attached to the portion of the catheter in which the radiation source is to be located. The centering balloon can then be inflated until it compliantly engages the vessel wall. In one embodiment, the centering balloon may be formed of helical lobes that substantially center the radiation source within the lumen of the vessel and allow perfusion past the catheter through a main spiral perfusion channel created between the helical lobes of the balloon.
However, it has been noted that single point failures can occur during use of the helical balloon structure, as well as in other structures with a continuous perfusion channel, such as spiral structures. Single point failures occur when an obstruction, such as plaque debris or a blood clot, block perfusion through the main spiral perfusion channel. As the helical structure uses compliant engagement to maintain positioning, portions of the catheter contact the vessel wall and prevent perfusion past the blockage through an alternate path. Thus, the obstruction can cause the perfusion flow rate, even with the helical centering catheter, to stop or to drop to such a low rate that the IRT must be discontinued until the area is recovered.
Thus, what is needed is an apparatus for improving perfusion in centering catheters with helical or spiral shaped base forms in order to mitigate the effects of single point failures.
The present invention includes a centering catheter for improved perfusion which has a centering segment with lobes which form at least one main perfusion channel, and a plurality of engagement knobs that compliantly engage the walls of the vessel and form auxiliary perfusion channels.